Article 1378

When it is absolutely impossible to settle doubts by the rules established in the preceding articles, and the doubts refer to incidental circumstances of a gratuitous contract, the least transmission of rights and interests shall prevail. If the contract is onerous, the doubt shall be settled in favor of the greatest reciprocity of interests.

If the doubts are cast upon the principal object of the contract in such a way that it cannot be known what may have been the intention or will of the parties, the contract shall be null and void. (1289)